Electric sorting by means of corona discharge

Abstract

A method for separating a particle mixture into a first and second fraction, the first fraction of particles having an electrical conductivity greater than the particles of the second fraction, by a) ionizing air to have the same polarity with a corona electrode; b) mixing the ionized air with a fluidized particle mixture containing two particle fractions with different electrical conductivities, to obtain a fluidized particle mixture ionized to have the same polarity; d) precipitating particles of the second fraction from the particle mixture on a collection electrode moving relative to the particle mixture, where the collection electrode is grounded or has an opposite charge to the corona electrode; e) removing particles adhered to the collection electrode as the second fraction; and f) obtaining the first fraction from particles of the particle mixture which do not adhere to the collection electrode.

1 . A method for separating particle mixtures into a first fraction and second fraction, wherein the electrical conductivity of the particles of the first fraction is greater than the electrical conductivity of the second fraction, the method comprising:
 a) ionizing air to have the same polarity with a corona electrode surrounded by air to be ionized;   b) mixing the ionized air with a fluidized particle mixture comprising two particle fractions with differing electrical conductivity, to obtain a fluidized particle mixture ionized to have the same polarity;   c) precipitating particles of the second fraction from the ionized, fluidized particle mixture on a collection electrode which is moving relative to the ionized, fluidized particle mixture and which is grounded or has an opposite charge to the corona electrode;   d) removing particles adhering to the collection electrode, thereby obtaining the second fraction; and   e) obtaining the first fraction from particles of the ionized, fluidized particle mixture which do not adhere to the collection electrode.   
     
     
         2 . The method of  claim 1 , wherein an airflow force is applied to the fluidized particle mixture prior to or after the ionization, and the particle mixture is supplied as a fluid flow in the direction of the moving or unmoving collection electrode. 
     
     
         3 . The method of  claim 2 , wherein the ionization takes place in a charge line through which the fluid flow is routed and in which the corona electrode extends,
 wherein the ionized fluid flow emerging from the charge line is directed at a collection electrode, and   wherein the particles rebounding from the collection electrode are collected as the first fraction and the particles adhering to the collection electrode are removed from the collection electrode as the second fraction.   
     
     
         4 . The method of  claim 3 , wherein the charge line is a pipe comprising an electrically insulating material, through which the corona electrode, which is embodied as a wire, extends in a coaxial fashion. 
     
     
         5 . The method of  claim 3 , wherein the charge line is a slit nozzle comprising an electrically insulating material, over the cross section of which a wire-shaped corona electrode beset with tips extends. 
     
     
         6 . The method of  claim 4 , wherein the airflow force for generating the fluid flow is applied to the fluidized particle mixture such that inflowing pressurized air is injected through a tapering nozzle into a mixing chamber connected firstly to the charge line and secondly to a tank which provides the fluidized particle mixture, the flow cross section of which mixing chamber being greater than the opening cross section of the nozzle. 
     
     
         7 . The method of  claim 2 , wherein the fluid flow emerges through a slit nozzle comprising electrically insulating material, in the surroundings of which a corona electrode in the form of a wire extending transversely with respect to the fluid flow is arranged such that the fluid flow is ionized when the third flow emerges from the slit nozzle, and
 wherein the ionized fluid flow which has emerged from the slit nozzle is directed at a collection electrode, wherein the particles rebounding from the collection electrode are collected as the first fraction and the particles adhering to the collection electrode are removed from the collection electrode as the second fraction.   
     
     
         8 . The method of  claim 2 , wherein the collection electrode is a stationary baffle plate. 
     
     
         9 . The method of  claim 2 , wherein the collection electrode is a revolving belt or a multiplicity of plates attached to a revolving chain. 
     
     
         10 . The method of  claim 3 , wherein the ionized fluid flow is directed at the collection electrode such that the ionized fluid flow impinges on the surface of the collection electrode at an angle that differs from 180°. 
     
     
         11 . The method of  claim 1 , wherein the fluidized particle mixture is a stationary fluidized bed,
 wherein the collection electrode is a rotating drum or a revolving belt, the drum or the belt is immersed into or at least contacts the fluidized, ionized particle mixture in sections, and   wherein the second fraction is removed from the belt or drum outside of the immersed or contacted region.   
     
     
         12 . The method of  claim 11 , wherein a pneumatic loading of a stationary fluidized bed is interrupted intermittently, and during the interruption, particles of a collapsed fluidized bed are collected as the first fraction and replaced by a further particle mixture comprising two particle fractions with differing electrical conductivity. 
     
     
         13 . The method of  claim 1 , wherein the fluidized particle mixture is a moving fluidized bed and the collection electrode is a rotating drum or a revolving belt, with the fluidized bed moving along a section of the drum or of the belt. 
     
     
         14 . The method of  claim 13 , wherein an airflow force is applied to the fluidized bed, thereby setting the fluidized bed into migratory motion in the direction of the collection electrode. 
     
     
         15 . The method of  claim 13 , wherein the fluidized bed moves through an inclined channel, at an upper end of which the particle mixture to be separated is provided and at a lower end of which the first fraction is collected, and
 wherein the collection electrode is embodied as a revolving belt, which, in one section, travels through the channel in the same direction as or counter to the moving fluidized bed and which, outside of the section, is cleaned of adhering particles in order to obtain the second fraction.   
     
     
         16 . The method of  claim 13 , wherein the fluidized bed moves through an inclined channel, at an upper end of which the particle mixture to be separated is provided and at a lower end of which the first fraction is collected, and
 wherein the collection electrode is embodied as a revolving belt, which, in one section, travels through the channel transversely to the moving fluidized bed and which, outside of the section, is cleaned of adhering particles in order to obtain the second fraction.   
     
     
         17 . The method of  claim 1 , wherein the corona electrode has a negative electric charge and the collection electrode is grounded or has a positive electric charge. 
     
     
         18 . The method of  claim 1 , wherein the particles adhering to the collection electrode are removed as the second fraction by applying an impulse load on the collection electrode. 
     
     
         19 . The method of  claim 1 , wherein the particles adhering to the collection electrode are removed as the second fraction by scraping. 
     
     
         20 . The method of  claim 1 , wherein the particle mixture is subjected to a mechanical screening process prior to fluidization, and a screen utilized for the screening is excited by an ultrasound oscillation in the range between 20 and 27 kHz. 
     
     
         21 . The method of  claim 1 , wherein the particle mixture is pulverized electrical scrap. 
     
     
         22 . The method of  claim 21 , wherein the electrical scrap comprises a photovoltaic element. 
     
     
         23 . The method of  claim 21 , wherein the electrical scrap comprises an electrode from an electrochemical cell. 
     
     
         24 . A method for separating electrical scrap, the method comprising:
 a) grinding electrical scrap to a grain size of less than 100 μm, to obtain pulverized electrical scrap;   b) pneumatic loading of the pulverized electrical scrap, to obtain a fluidized particle mixture; and   c) carrying out the separation method of  claim 1 .   
     
     
         25 . An appliance comprising:
 a) an inclined channel comprising an air-permeable base to which pressurized air is applied and which comprises a multiplicity of corona electrodes;   b) a metering apparatus arranged at an upper end of the inclined channel, wherein the metering apparatus supplies a particle mixture comprising a first fraction and a second fraction, wherein the electrical conductivity of the particles of the first fraction is greater than that of the second fraction to the inclined channel;   c) a collector that collects the first fraction, arranged at the lower end of the inclined channel;   d) a revolving runner that runs in the inclined channel in sections; and   e) a scraper arranged on the runner outside of the inclined channel, that scrapes off particles adhering to the runner as the second fraction.   
     
     
         26 . The appliance of  claim 25 , wherein the runner is embodied as a belt and the revolving belt runs up the inclined channel along the inclined channel. 
     
     
         27 . The appliance of  claim 25 , comprising a multiplicity of runners which run transversely through the inclined channel and are respectively embodied as a belt; and
 a revolving cleaning belt which runs parallel to the inclined channel,   wherein scrapers are provided in a crossing region of cleaning belt and runners, which scrapers clean off particles adhering to the runners as the second fraction and supply said particles to the cleaning belt to be transported away.   
     
     
         28 . The method of  claim 1 , wherein the particle size of the first and the second fractions is less than 100 μm.